The invention relates to a method for improving filament cohesiveness of chopped aramid fiber.
Thermoplastic pre-compounds filled with aramid fibers (generally, up to 20%) and in the form of granules are frequently used as basic material for the manufacturing, for instance by an injection-molding process, of composite articles (e.g. gears, bearings) with an improved resistance to abrasion. These pre-compounds are produced by mixing thermoplastic matrix material as chips with chopped aramid fibers via a melt extrusion process. To that end, the thermoplastic chips and the chopped aramid fibers are separately dosed into the throat of an extruder. A serious problem of feeding fibers into the extruder is the forming of bridges and lumps of fiber, hampering smooth and fast introduction into the extruder. It appears that single filaments that are not longer bound in the chopped pieces of fiber, are agglomerating into fuzz balls, which lead to lumps, bridging, and clogging of the transport systems.
It is therefore an object of the present invention to provide a method for obtaining chopped fibers that do not have these disadvantages. Thus the present method provides in granule like chopped fibers, i.e. fibers wherein the cohesiveness of the filaments of one fiber is improved which results in a behavior as if the fiber is one big monofilament. It is however, not possible to alleviate the above-mentioned disadvantages by applying improved binding agents or the like, because this does not lead to a substantially improvement of the filament bundle cohesion.